Nose Gear Question?

I have seen Roberta's approach to "staking" the outer bearing bushing to the nose wheel yoke; thus allowing her to set the correct bearing preload and not have the bushing turn instead of the bearings. I believe this was on the the earlier style of nose wheel yoke.

Has anyone "staked" the bushing with the later yoke design which has less surrounding metal and also a lightening hole? If so what location did you use? Edge distance?

Thanks

Bob Barrows has done his new style fork. I don't know what the dimensions were, though. I placed mine half way from the inner diameter to the outer diameter of the mushroom. I think that would be fine even for the new fork. Place the hole where you have the greatest mass of material in the fork, like more forward towards the leg swivel. The hole is so small I doubt it would affect the strength. I used # 10-32 countersunk screws and tapped the mushrooms instead of the fork. I did not want sharp edges in the holes in the fork that might produce stress risers and possibly develop cracks. I'm sure Van's could advice if this is improper.

Roberta

Thanks Roberta,
I guess that is why I asked. That is, right at your "half way" position on the new yoke is a lightening hole. But as you say, hole is small enough that strength may not be affected. I will need to use slightly ifferent process as mne is RV-6A with new yoke. I'll see if I can contact Bob Barrows.

robertahegy said:

Bob Barrows has done his new style fork. I don't know what the dimensions were, though. I placed mine half way from the inner diameter to the outer diameter of the mushroom. I think that would be fine even for the new fork. Place the hole where you have the greatest mass of material in the fork, like more forward towards the leg swivel. The hole is so small I doubt it would affect the strength. I used # 10-32 countersunk screws and tapped the mushrooms instead of the fork. I did not want sharp edges in the holes in the fork that might produce stress risers and possibly develop cracks. I'm sure Van's could advice if this is improper.

Roberta

Click to expand...

I did

the same thing with the new style fork. Looks fine after 100 hours..

Wait a minute...100hours since September...Woah!..

Frank

Sounds Good. I am thinking of putting it where the red dot is:

frankh said:

the same thing with the new style fork. Looks fine after 100 hours..

Wait a minute...100hours since September...Woah!..

Frank

Click to expand...

Nose gear stake.

I'm a bit (maybe more than a bit) cautious about mods so I did a bit of research on this one. I contacted several builders who had used 10-32 stake screws in the nose gear in both 6As and 7As. There were no reports of problems. One builder had staked a 6A at the 3 OClock position 6 years ago with no reported problems and had more recently staked a 7A in the same position.

Then I asked Vans for comments. They said that there were many examples flying with the stake and they had not heard of any adverse feedback. They were not opposed to the concept. They did suggest however that a smaller screw could be considered and there is merit in that recommendation.

In the end however I went with a 10-32 AN countersunk structural machine screw due to precedence, availability, and the fact I could get it in 100 degree CS head and with exactly the right grip length. It's also 125,000 psi so no chance of failing.

The exact screw is an AN 509-10R12 or an MS 24694-S54.

I have attached a photo of the final arrangement. The screw is prevented from backing out by the fairing bracket that eventually covers the screw head. The forks are snug reamed and the mushrooms are tapped. You'll need a #21 drill and a 10-32 tap. It's easier if you have a tapered tap to start with and follow up with either an intermediate or bottom tap.

The best way to do this is to temporarily bolt the mushroom to the fork and pilot drill them both together while properly fixed in a pedestal drill and properly aligned to ensure the drill is orthogonal to the forks.

If you do this with a hand drill you are almost certainly doomed to be disappointed.

I placed the screw exactly mid distance between edge of the axle bolt hole and the edge of the fork in the 6 OClock position (my photo is upside down).

I noted that some people with early 7A kits had the original nose gear and at least one (Roberta....who exhibits quite a lot of intuitive rat cunning when it comes to matters structural...but who has absolutely no idea of her taxi speeds !!!) staked at the 9 OClock position. That makes the most sense for that model. However the more recent modified nose gear (which I have) has a lightening hole at the 9 OClock position which changes things.

It will need to be appreciate that the loads on the nose wheel which are then transmitted through the axle and fork are both dynamic and complex. It is possible for those loads to arise from different directions depending on the circumstances meaning that the fork plates will be subjected to loads that are horizontal, vertical and lateral.

I am not making any recommendations here. I am just reporting what I have done. It is up to others to do their own research.

"Intuitive Rat Cunning"? What's with that? Is it a good thing?

You must have used that to determine your stake location. Looks good to me.

Generally, I try to stay below rotation speed while taxiing. But I do hold the stick back.

Roberta

Grayhawk,

I have the new fork on my 9a and have the mushroom spacer "staked" with a #10-32 flush phillips structural screw as do others. I located the hole in the fork (unthreaded but snug--threads are in the spacer) at about the location you mark with the dot. I placed mine there at the 10:30 position vs the lower 8 o'clock position to reduce any "stretching" loads (vs compression) due to a hard landing. I have 112 hrs on the plane now, just went thru its first inspection and all looks good. BTW, I also called Vans before doing this and they had no objection.

Cheers,

db

Thanks

Thanks to all who replied. My "red dot" position was selected to have the most surrounding metal and since there are two of these locations, I picked the upper one for the stated reasons of compression versus expansion. But it would look like there is enough empirical data to support several positions.

So the theory is the nosewheel bolt doesn't need to be as tight if the spacers are staked to the fork? This is supposed to help with shimmy, or something else?

I found

that to stop the spacers rotating the bolt had to be pretty tight. Tight enough that it was giving significant drag to the wheel.

This is quite a preload on the bearings and personally I 'd rather have my wheel rotate freely.

It is possible the extra drag was setting off the "porpoising" we saw in the video.

Thats my theory anyway.

frank

Preloading the bearing as Van's instructs was meant to create enough friction to prevent the bearing "mushrooms from turning and prematurely wearing. This also created excessive drag on the wheel, which slowed the acceleration of the wheel on touchdown. It was supposed to free up with time, but often does not.

The excess drag, as the wheel touches down, causes deflection of the leg and deformation of the tire, much like landing with a nosewheel brake applied. Low tire pressure and/or close fitting wheel pants adds to the problem as the tire can splay out and grab the wheel pant, creating a jamming situation that can literally flip the plane on it's back.

Staking the mushrooms allows you to properly load the bearings. This allows the wheel to rotate more freely and not tend to grab as hard on touchdown.

Proper tire pressure, adequate tire/ pant clearance, a wheel that is free to spin up properly on touchdown, and good technique will help ensure that your prize bird keeps the canopy side up on landings. And takeoffs.

Roberta

Another option?

robertahegy said:

Preloading the bearing as Van's instructs was meant to create enough friction to prevent the bearing "mushrooms from turning and prematurely wearing. This also created excessive drag on the wheel, which slowed the acceleration of the wheel on touchdown. It was supposed to free up with time, but often does not....

Click to expand...

I am not at this point so this suggestion may be just so much hogwash but, wouldn't a properly sized spacer placed between the two mushrooms allow tightening the fork bolt to it's full rated torque without over preloading the bearings? That way the mushrooms would be really snug, preventing their rotation.

-mike

That would work in a perfect world, but due to variations in MFG tolerances, it would be hard to make the correct size spacer for every application. Shimming is possible, but that might be more troublesome than just simply staking. I would have liked to see something more like my Cherokee fork, as that setup seemed to work well, but it requires a lot of machining. I think Van's made an economical fork that works well with just a simple tweek like the stakes.

Roberta

robertahegy said:

"Intuitive Rat Cunning"? What's with that? Is it a good thing?
Roberta

Click to expand...

Yep...a VERY good thing.